Heterogeneity in Habitat Trends Among Circumpolar Caribou and Reindeer Herds

We used bi-weekly NDVI composites to estimate the strength of trends in habitat conditions of circumpolar Rangifer populations 1982-2007. Positive trends in relative greenness in early summer were strongest for arctic mainland calving grounds, yet there was substantial heterogeneity within and between continents. There was little evidence of habitat trends within winter ranges of these herds in taiga. Early green-up and increased relative plant biomass during peak lactation demand by Rangifer females were associated with increased calf survival during June and increased autumn weights of calves within the circumpolar region. Regional variability in early summer vegetation phenology across the circumpolar North was closely associated with the spatial variability of springtime atmospheric circulation patterns. Heterogeneity in circumpolar habitat trends implies associated heterogeneity in Human-Rangifer systems performance.